#define  _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	int i = 0;
	int s = 0;
	int each = 1;
	for (i = 1; i <= 20; i++)
	{
		each = i * each;
		s = each + s;
	}
	printf("%d\n", s);
	return 0;
}